Process of heat control in catalytic hydrogenation reactions



B. J. c. VAN DER HoEvEN 2,515,279 PROCESS 0F HEAT CONTROL IN CATALYTIC HYDROGENATION REACTIONS July 18, 1950 4 Sheets-Sheet 1 Filed sept. 2o, 194e B. J. c. VAN DER HoEvEN 2,515,279 PROCESS oF HEAT CONTROL 1N CATALYTIC `July 18, 1950 HYDROGENATION REACTIONS 4 Sheets-Sheet 2 Filed Sept. 20, 1946 l INSIDE DIAMETER OF TUBE IN INCHES zo so WEIGHT ENzENe I N VEN TOR.

July E8, 1950 B. J. c. VAN DER Hom/EN 2,515,279

PROCESS OF HEAT CONTROL 1N CATALYTIC RYDROGENATION REACTIONS Filed Sept. 20. 1946 4 Sheets-Sheet 5 i. Z Il ING VALVh CONDENSEJE 22C EIVEE.

HY URO@ ENATE COOLER.

HEATER VA 902x122 HYDROGE LIGA) I D PROHYDQOGENATE:

WITNESSES: INVENTOR ff/Ma JC ww pff bfvf/v July E8, 1950 B. J. c. VAN DER HOEVEN M5279 PRocEss oF HEAT CONTROL TN CATALYTTC HYDROGENATION REACTIONS Filed sept. 2o, 1946 4 sneetssheet 4 WNNVI www1 INVENTOR 55E/wma J. C. wmf u@ Hof @ff/v ATTORNEY WITNESSES:

Patented July 18, i950 PROCESS 0F HEAT CONTROL IN CATALYTIC HYDROGENATION REACTIONS Bernard J. C. Van der Hoeven, Beaver, Pa., as-

signor to Koppers Company, Inc., Pittsburgh, Pa., a corporation of Delaware Application September 20, 1946., Serial No. 698,381 l 7 Claims. l

'I'his invention relates toheat control in catalytic hydrogenation reactions, and is more particularly directed to the application of novel heat control methods in processes for vapor phase catalytic hydrogenation of aromatic compounds, especially in the manufacture of cyclohexane by vapor phase catalytic hydrogenation oi' benzene.

Many catalytic hydrogenation reactions such as the vapor phase hydrogenation of aromatics such as benzene and naphthalene and their derivatives and homologues are strongly exothermic and require some form of heat control to keep the cataiyst within its effective range of hydrogenation temperature; Close control or temperature requiring the rapid removal' of large quantities of heat from the catalyst is required in order to avoid development' of hot spots which cause excessive deterioration of the catalyst and in order to avoid objectionable side reaction which degrade the desired product.

Various methods for controlling the temperature of the catalyst in hydrogenation catalysis have been suggested and/or utilized in the prior art. These usually involve a heat exchange type converter of suitable design using such heat transfer media as water under pressure,I mercury, sulfur, and like heat transfer uids. The present invention does not differ from the prior art in this respect but as will appear more particularly hereinafter utilizes such heat transfer iluid to remove the heat of catalysis from the'A catalyst.

*,I'he diiculty with the prior 'art methods is that no matter how eiective a heat transfer medium is employed, the maximum eillciency of the heat exchange type converter islimited by the rate at which heat may be dissipated from theicatalyst, which is not very greatlconsiderlng the low thermal conductivity of the common carriers used in hydrogenation catalysts. "It has been necessary, therefore, in accordance with the prior art practices to utilize heat exchange ype converters having small tubes; say aboutli inch or lessin diameter, or similarly constructed heat exchange converters in which the catalyst is so distributed with reference tc the heat transfer iluid that'the heat of catalysis need only travel through a small layer oi.' catalyst to reach the heat transfer fluid. Thus it has been necessary in the prior art to utilize especially designed equipment to accommodate the peculiar heat conditions in a hydrogenation catalysis.

'I'he present invention has for its objects to provide novel methods of temperature control in vapor phase catalytic hydrogenation reactions. to

provide ecient means tor dissipatlng the heat of the reaction in such processes, to provide simple and effective processes for making cyclohexane by the catalytic hydrogenation of benzene, to provide processes in which'the size and distrlbution of the catalyst mass is relatively non- 'criticaL to avoid the disadvantages of the prior art and to obtain advantages as will become apparent as the description proceeds.

These objects are accomplished in the present invention by carrying.u out the catalysis with a procatalysate consistingpredominantly of inerts. Bycarrying out the catalysis with a procatalysate consisting predominantly of inerts, of example, a procatalysate consisting essentially oi prohydrogenate vapor and hydrogen in hydrogenating proportionsin admixture with an inert gas in the proportion of at least 2 mols or volumes of inert gas for each mol or volume of prohydrogenate vapor, I am able to obtain effective hydrogenation catalysis in processes in which the size and distribution of the catalyst mass is such that the heat transfer rate within the catalyst mass is insuiiicient to carry oi the heat of catalysis when the catalysis is carried out without the inert gas or with at most a minor proportion thereof.

In describing the invention the term prohydrogenate" will-be used to refer to the material which is hydrogenated, the term hydrogenate to the material produced, the term procatalysate to the material fed to the converter, the ttrm catalysate to the material eflluent of the converter and the term "catalant$ to the materials involved in the conversion. Thus in the hydrogenation of benzene, benzene is the prohydrogenate, cyclohexane is the hydrogenate, the mixture of benzene, hydrogen and inert gas is the procatalysate, the mixture of cyclohexane, hydrogen, etc. eiliuent of the converter is the catalysate and the benzene and hydrogen are the catalants.

While it has heretofore been determined that the rate of hydrogenation of benzene is inversely proportional to the amount of cyclohexane vapor present when "suitable mixtures are passed through a thin layer of catalyst at atmospheric pressure (C. A. 37, 4614 (1943)), the present invention does not depend entirely for its efilcacy upon a lowered rate of hydrogenation per se, but produces results entirely disproportionate thereto. The processes of the present invention, moreover, are conducted at superatmospheric pressure to inhibit the reverse reaction which is largely responsible for the effects noted in this reference.

When procatalysate, properly constituted and proportionedV in accordance with the invention, is passed in the vapor phase at superatmospheric to use much larger masses of catalyst than was possible in the prior art. As the volume ofgas, which passed through the catalyst mass per unit of hydrogenate produced, is increased by dilution with an inert gas, a critical velocity is obtained in the catalyst mass at which the heat transfer eillciency is significantly increased. 'Ihis effect is significant when the major portion of the procatalysate is an inert gas and becomes marked when the dilution reaches 2 or more mols or volumes of inert gas for each mol or volume of prohydrogenate vapor and increases exponentially as the rate of throughput is further increased by further dilution.

It is possible, therefore, in accordance with the invention, to utilize heat exchange converters having substantially larger tube diameters and substantially larger cross sectional area of catalyst through which heat must be dissipated to the heat transfer fluid than in the prior art methods. Thus the present invention makes it possible to utilize heat exchange converters of simpler and more economical design. Moreover, the processes of the invention are readily adaptable to a wide variety of heat exchange converters making it possible to utilize stand-by equipment even though not especially designed for hydrogenation catalysis in accordance with the prior art methods.

The invention may be more fully understood from the following detail description taken with reference to the accompanying drawing in which Figure I is a flow sheet of a simplified form l of the invention, Figures II and II are curves illustrating qualitatively certain aspects of the invention, Figures IV and V are ow sheets illustrating typical embodiments of the invention and Figure VI is a detailed view of a modified form of Figure III.

While the invention is applicable to hydrogenation catalysis of a wide variety of materials such as benzene, toluene and like hydrocarbons of the benzene series; naphthalene, methyl naphthalene and like hydrocarbons of the naphthalene series; phenol, cresols, napthals, etc.; and olefins where the heat of the reaction is big enough to be a problem, and particularly aromatic hydrocarbons, it is most suitably illustrated with refer- Such a procence to hydrogenation of benzene. ess and apparatus suitable for carrying it out are l illustrated diagrammatically in Figure I. The z process is carried out as follows:

Benzene and cyclohexane are mixed in the desired proportions in supply tank 2, elevated to the operating pressure and temperature by pump 4 and heater 6, and then passed through line 8 to converter I0. Simultaneously, hydrogen is elevated to the operating pressure and temperature by compressor I2 and heater I4 and passed through line I6 to the converter I0.

within the limits of practicability may be used. l Lower pressures, though preferably not lower than about 50 pounds per square inch gauge, may be used since any pressure above atmospheric tends to suppress the reverse reaction. Where cyclohexane is used as the diluent, it is impory these principles, will readily be able to determinerwhat pressures are' required in any particular case to effect substantial suppression of the reverse reaction.

'Ifhe converter l0 consists of a 3 inch pipe or tube I8 surrounded throughout the major portion of its length by a water jacket 20. In the bottom of tube I8 there is provided a catalyst support 22 projecting upwardly to a point several inches above the bottom of the water jacket 28. The tube I8 is packed with catalyst pellets, as shown by the hatching, to within a few inches of the top of water jacket I8, and the over-al1 dimensions are 'such to provide a catalyst mass 3 inches in diameter and 84 inches long.

Temperature regulation in the converter is obtained by circulating a suitable heat transfer fluid such as Water under pressure, or Dowtherm, through the water jacket 20. The heat transfer uid is withdrawn through lines 24 and 28 to the cooler heater 28 through reservoir 38 or by-pass 32 and returned to the water jacket 20 through lines 34 and 36 by means of pump 38. Make-up water is introduced into reservoir 30 by means of pump 40 and maintained at the desired operating pressure; for example, at about 200 pounds per square inch gauge. The reservoir 20 which serves as an expansion tank is not needed when Dowtherm is used. Hence, when Dowtherm is used as the heat transfer fluid, valve 42 and 44 are closed and valve 46 opened to by-pass the reservoir. Cooling water or steam may be sued to heat or cool the heat transfer fluid in the cooler-heater The eilluent of the converter I8 is passed through line 48 to condenser 58 and the condensate is-collected in the product receiver 52. Hydrogen and other non-condensibles, for example, methane, are vented at 54.

Operation of the described process under a wide variety of conditions within the scope of the invention is illustrated in the following tables: 'I'he data of Table I were obtained using water as a heat transfer fluid;` whereas the data of Table II were obtained by using Dowtherm. In each case the procatalysate mixture containing benzene in the indicated proportion (parts are by weight throughout the specification except where otherwise specified) a 50% excess of hydrogen and the balance, cyclohexane, was passed through the elongated catalyst mass at the indicated space velocity while maintaining the catalyst mass within its effective temperature range by circulati ing the heat transfer fluid through lthe jacket 2l at the indicated temperature.

The catalyst was reduced nickel mounted on kieselguhr.

It is suitably prepared as follows: Nickel carbonate-kleselguhr is precipitated by 'freezing point method.

guhr is water free. Thel powder'is mixed with I8 and given a further reduction with hydrogen at 200 C. at atmosphericl pressure.

. 4% ef graphite and fabricated. 1n the 1er-111:01v4

i tied, thefpercentage oi benzene isdetermined by the Acid Heat Test" in whici`1`f`the amountw!A benzene presentv isncorreiatea with' the hasta: f

nitration by an empirical curve. 'I'his'test usually indicates a slightly' higher purity than th'e trees-fV ing point methodrhowever. 'at purities 'of 99%.

the diiierence isV usually not more than 0.2%.

Under conditions of; comparable and continuedoperations `the 'cyclohexane would'passthroush the converter iive or six times and consequently the impurities would Anot exceed 1.25 to 1.5%.

Table -I v Feed speee ver. Temperature.' o.

Het spei. Predm..." Run Wt P CM'IP' Catalyst' Percent te" '115151, P-s' can Temi. Jacket 11511.111ehe5 oyen. f G.1 .H. only Liquid. Inlet Inlet Max.

A 4.50 75 '0.151 2.01 .I 147:: 127 231 1s 09.7 s 1 4.55 75 0,2527 1.01 145 .I 129- 252- 1s 100.0 o. 21.5 5.00 75 0.410 .v 210 135 :122 200 1s., 100.0 D 21.0 4.94 75 A-0.400 2.01 110 11211 205 24-30 99.8 E 25.5 4.07 75 0.447 2.00 110 110 27a 15-24 00.0'

Table-II Feed Spa Vel. Temperature/T.

' Hotspot Piedini. Run wt' Per .ca' 1P? Catalyst.' L0ca- Percent' ent Temi. P' 0.11.y 'remi Jaekei mamelles oyeie.- CoH .P. H. Only -Liquid Inlet Inlet Max F. 10.0 7.5 75 .0.282 5.15.: 14s 125.'` 224 a0 99.0 o 10.1 14.0 0.525 5.50 144 127- 215 50-00 00.5- H 14.7 12s- 75 1. 0.712 5.38 145 11s 252" j s0 1 00.0. I 15.2 8.0 75 :0.450 l:1.50 150 18s 250 1a 00.5 J 15.4 18.1 75 1.054 7.51 151 y 130 24e .2o-a0 29.0,v K 10.5 12.0 75 0.508 5.05 140 121 275 .5o-a0 100.0 L 25.0 11.1 s0 1.050 4.40 15a 102 202 1s-24 00.0

The date given in the ebpve-tabi-es shewgeriir11 Figuren 'tnereis 'enema eurve'iuuspratig' cient operation'over a wide-rangeogconditions. the relation vbetween the feed composition.' and: Y They show thatrthe space velocity,r -tlgured as the permissible'tube siz.'"'lh'e datais g'ured'on volumesof liquidjper vol-urnel of catalyst, per hour, the basis of an 8 4? catalyst bed with' a. rate or may be varied over a, wide'l range without adthroughput suicient tohydrogenate'zgallons of versely eiectingthe operation, thusthe benzene 45. benzene per hour. For-a. 3 inch tubetliisgures space velocity was varied from 0.18 'to 1.06am! y the total liquid space'velocity was A.varied from"- about 2 to a little over 7.5. This greatiilexibility operation is characteristic of the processesof the tube diameter is around 1 in. With larger diameter tubes the -temperature intheA catalyst mass becomes excessive. Efforts to carry out the reac-f tion in 11.1/ in. tubes without a diluent gas proved unfeasible because of fusion in the catalyst mass.

It was determined also under comparable conditions that cyclohexan'e could be recycled without objectionable build-up of impurities due to decomposition or isomerizatlon of the cyclohexane. Thus, startingf'with' a feed mixture containing 18.25% benzenev and the balance cyclohexane of 99.65% purity and recycling product cyclohexane, it was determined that after two passes the purity dropped to 99.25%,` after four` passes to 98.9%, after 6 passes to 98.65%, and after 8 passes to 98.45% as'determined by the- (Unless otherwise specido not diier" signicantly from the proportions byv volume, or inother words from the molar proportions. Thus for 30% benzene the'weight proportion is 2.2 parts of'cyclohexane for each part "of benzene, whereas the mol proportion is 2.1'fmols of cyclohexane for each mol of benzene.

Figure HI -plots the" second' derivative of the curve of Figure n. or"in other words, the first' derivative of the slopeof the curve of Figure H, and thereiorerepresets the rate of change of slope of the curve oliia'ure H. it showsthat the rate of change of'slope reaches a rriaxirriiiin` at about 30% 'benzene'."the point where critical effect of? the diluent becomes marked.

From inspection oi the curves of Figures Il; sind.v m it will be seen that thepermss'ible tube "Size: increases very slowly as-cyclohexane is addecifto" the procataiysate down tri-about 30% benzene" and that thereafter the permissible tube' size iin-:i creases very rapidly. it is thus possible 4to oper 7 ate in accordance with the invention with converters having tubes significantly larger than heretofore considered practical in the prior art.

Another advantage of operating within the limits of the invention which is not apparent from the curve but which is amply illustrated in the data given in Figures` I and II is that within the limits of the invention. tube size is substantialiy less critical than in the prior art processes. Thus while the curve of Figure I shows that a benzene concentration of 15% is most desirable for a 3 inch tube and a benzene space velocity of 0.78 the data of Tables I and II show great ilexibility of operation over the range of 10 to 25% benzene. If the weight percent of benzene were held constant, say at it would be possible to eect a correspondingly wide variation in the tube size. Of course, any tube less than 3 inches in diameter could be used. A larger tube can also be used, depending upon the efficiency of the heat transfer fluid and the rate of throughput Aand the desired conversion of benzene to cyclov prior art method it was not feasible to use a tube as large as 11/2 inches in diameter.

The invention may be more fully understood with reference to particular embodiments theremg erected m converter se may be simply and effectively controlled.

In carrying out processes according to the invention and illustrated vin'lligure IV, liquid prohydrogenate is brought to the operating pressure characteristic ofl the particular hydrogenation catalysis by means of a suitable pump Il and passed through line 80 into vaporizer 58 where it is vaporlzed by indirect heat exchange with the catalysis through the instrumentality of the heat transfer circuit described above. Simultaneously hydrogen at the operating pressure and in hydrogenating proportion to the liquid prohydrogenate is brought into admixturewith the prohydrogenate vapors. Intimate admixture.

is advantageously obtained by bringing the hydrogen through line 82 into the bottom of the vaporizer 58. Part of the required hydrogen is recycled hydrogen as will be more particularly described and the remainder from any suitable source is elevated to the operating pressure by means o f a suitable compressor 84 and introduced into the system byline 88.

The eiuent of the vaporizer 58 passes through z line 88 into the heat exchange converter 56 where the catalysis is effected. Heat of catalysis is transferred to the heat transfer fluid and in turn transformed to heat of vaporization in the vaporizer 58 and/or dissipated in the condenser 50 and cooler 1l.

The mixture of hydrogenate vapor and hydrogen eniuent of the converter 55 is divided into two portions; one portion, the quantity of which is determined by thesetting of valve 90, is reof by referring to the flow sheets illustrated in prohydrogenate vapor in passing through the tubes passes through an elongated mass of catalyst. Suitable means including lines 62 and 64 are provided for circulating a heat transfer fluid about the tubes of the converter in order to maintain the catalyst mass in the tubes within its eiIective range of temperature.

Heat transfer fluid from converter 56 is passed through line 64 into vaporizer 58 where at least a part of the heat absorbed from the catalyst is utilized to vaporize liquid prohydrogenate and, if desired, liquid hydrogenate. The heat transfer iluid is withdrawn from the vaporizer 58 through line 66 and circulated by means of pump 68 through the heater cooler 10 and/or by-pass V12 to line 62 to complete the cycle of heat transfer fluid. The heater cooler 10 'is so designed that it may be used as a heater during the start-up period when it is necessary to bring the catalyst Suitable means for reducing the pressure is provided at |04 or, if desired. in line |06 and vent According to this form of the invention it will beseen that the hydrogenate required as a diluent for the reactant may be recycled either in the vapor phase or in ,the liquid phase, though a more suitable system for accomplishing the latter is illustrated in Figure V which will be subsequently described. According -to the form of the invention shown in Figure IV it is contemplated that the major portion, if not all of the recycled hydrogenate is recycled in the vapor phase.. This has the advantage of simultaneously recyclingy the bulk of the excess hydrogen as well as materially reducing the load on condenser 60. Since it is desirable that the feed mixture shall contain at least 2 mols or volumes of hydrogenate for each mol or volume ofprohydrogenate as more fully set out above, it follows that at least of the hydrogenate eiliuent of the converter 60 must be recycled. By recycling all, or substantially all, of this in the vapor phase, a very marked reduction in the load on the condenser 60 is eiected. This makes it possible to use a condenser of a much smaller capacity than if all of the hydrogenate eiuent of converter 56 were to pass through the condenser, and has the advantage that it is cheaper to dissipate heat of a reaction in an ordinary cooler such as is contemplated at 10 than in a condenser.

It is desirable, according to one form of the invention, that the condenser 60 shall have inadequate capacity to condense all of the hydrosenate emuent vof the converter and that at h Y formed as a result oi' the hydrogenation catalysis.

As above noted, Figure V illustrates a process in which the recycled hwdrogenate may advantageously be recycled in the liquid phase.

The general arrangement of theA apparatus is the same as in Figure IV and like reference numerals are used to designate like parts. The principal difference lies in the method of recycling excess hydrogen and the recycled hydrogenate.

The mixture of hydrogenate and hydrogen eilluent of converter 56 is passed through the condenser 60 into high pressure receiver ||0 where a separation between the condensed hydrogenate and noncondensibles, including excess hydrogen, is eilected. The noncondensiblesA are passed through lines ||2 and ||4 by means of a pump H6 back to line 02, thus completing a cycle whereby excess hydrogen is recovered. A portion of the noncondensibles is vented through reducing valve ||0 in order to purge the system oi' any gaseous by-products of the catalysis.

The liquid hydrogenate from receiver ||0 is divided into two portions, one of which is passed through reducing valve into low pressure receiver |22 as product, and the other of which is passed through lines 98 and |00 by means of pump |02 to line 00, thus completing a cycle.

If desired, a portion of the mixture of hy-f drogenate and excess hydrogen may be bled oil through valve |24 and line |20 to the inlet side of pump I6.

It will be observed that in accordance with this form oi' the invention, substantially all of the recycled hydrogenate is recycled in the liquid phase. This has the advantage oi.' increasing the proportion of the heat of catalysis which is transformed to heat of vaporization in the vaporizer 58, and in fact, under ideal conditions, the proportion of hydrogenate recycled `as liquid to thf` liquid prohydrogenate may be such that all of the heat of catalysis in excess of normal losses may be transformed into heat oi vaporization. When the desired proportion of hydrogenate to prohydrogenate is such that the heat of catalysis is not sumcient to effect vaporization of both, part of the recycled hydrogenate may be recycled in the vapor phase through line |26, or the cooler-heater 10 may be operated as a. heater to supply the necessary heat. Operation in this manner has the advantage that only one piece of apparatus, namely the condenser is required to efl'ect dissipation of the heat of catalysis. This provides simplicity and ilexibility of operation. For example, with adequate cooling capacity in the condenser 60, valve 16 may be closed oi! completely so as to by-pass the cooler-heater 10 and temperature control in the process effected by suitable adjustments in valves |24 and |28. y

How this type of control may be still further simplified is illustrated in Figure VI wherey separate condensers 60-A and 60-B are utilized to condense the recycled hydrogenate and the product hydrogenate respectively. By suitable adjustment of valves |30 and |32 the proportion of recycled hydrogcnate to product hydrogenateI is determined. Thereafter, all that is necessary to effect temperature regulation in the process is to adjust the setting oi valve 12d- A which may be done either manually or by suitable automatic control devices.

The i'orm of the invention illustrated in Figure V is further of advantage. in that it is well adapted to the use of an inert gas such as nitrogen for the diluent for the prohydrogenate. Nitrogen may be introduced along with the hydrogen or separately by a suitable compressor, not shown, to take the place of recycled hydrogenate. It is then separated from the ,hydrogenate in condenser 80 and high-pressure receiver ||0 and recycled through lines ||2 and III back to line 02. The amount oi' nitrogen which need be introduced/ into the process initially will be that required to give at least two volumes of nitrogen in the eilluent in the vaporizer l0 to each volume of prohydrogenate vapor. Thereafter the amount which need be introduced will correspond to the amount vented at ||0 and need be only suilicient to purge the system from accumulations of uncondensible gases formed in the catalysis.

Unless otherwise specified the parts are by weight and pressures are in pounds per square inch gauge.

While I have described my invention with reference to particular embodiments thereof it is to be understood that they are given by way oi' illustration only and that variation may be made therein without departing from the spirit and scope of the inventionl as described herein and set forth in the appended claims. Thus while I have described my invention with reference to vapor phase hydrogenation and while the eilects of diluent hydrogenatea especially pronounced in vapor phase hydrogenations, nevertheless some of the objects of the invention are accomplished in liquid phase hydrogenation -where the catalysis is effected in the presence of a major proportion of hydrogenate and at a pressure above atmospheric suillcient substantially to suppress the reverse reaction.

I claim:

l. In a process for vapor phase hydrogenation catalysis in a single stage heat exchange converter of the jacketed type wherein a heat transfer fluid is circulated through said Jacket in contact with the walls of the catalyst-containing units in indirect heatv exchange through said walls with the catalyst therein and to and from means for regulating the temperature of the heat transfer fluid and wherein the transverse dimensions of the catalyst mass in each said unit are not substantially less than 1% inches and not substantially greater than 5 inches and the length of said catalyst mass in each said unit is at least four times the minimum transverse dimensions, whereby the distance heat of catalysis has to travel through the catalyst mass to reach said walls is so great that overheating of the catalyst mass results when the procatalysate consists essentially of prohydrogenate and hydrogen in hydrogenating proportions, the improvement which comprises preparing a gaseous mixture consisting essentially of prohydrogenate vapor and hydrogen in hydrogenating proportions in admixture with a recycled inert gas in the proportions of at least 2 mois and less than 10 mois of inert gas for each mol of prohydrogenate, passing said gaseous mixture through said catalyst mass at a rate which gives substantially complete conversion and at a pressure sumcient to suppress dehydrogenation of the product while throughput is between about 2 and '1.5 nquid v01- umes of benzene and cyclohexane per volume of catalyst per hour.

4. The process of claim 1 in which liquid prohydrogenate and liquid hydrogenate are vaporized by indirect heat exchange with the heat transfer iluid to provide in part said gaseous mixture and in which the quantity of liquid thus vaporized is such that the heat of vaporization substantially equals the amount of heat of catalysis transferred to the heat transfer medium.

5. The process of claim 4 further Acharacterized in that the catalysate is divided into two streams.

Athe first of which contains hydrogenate in an amount substantially equivalent to the prohydrogenate, the hydrogenateof this stream is condensed as product, the second stream is divided into third and fourth'streams, the third stream is recycled to the catalysis without substantial change in temperature and pressure as part of the recycled inert gas. the hydrogenate of the fourth stream is condensed and returned to the evaporating step to provide the balance of the recycled inert gas whereby the temperature of the heat transfer fluid may be regulated by adjusting the relative flow of catalysate in the third and fourth streams.

6. The process of claim 4 in which the prohydrogenate is benzene and the recycled inert gas consists essentially of cyclohexane.

7. The process of claim 6 in which the rate of throughput is between about 2 and 7.5 liquid v01- umes of benzene and cyclohexane per volume of catalyst per hour. l

BERNARD J. C. VAN DER HOEVEN.

REFERENCES CITED The following references are of record in the 

1. IN A PROCESS FOR VAPOR PHASE HYDROGENATION CATALYSIS IN A SINGLE STAGE HEAT EXCHANGE CONVERTER OF THE JACKETED TYPE WHEREIN A HEAT TRANSFER FLUID IS A CIRCULATED THROUGH SAID JACKET IN CONTACT WITH THE WALLS OF THE CATALYST-CONTAINING UNITS IN INDIRECT HEAT EXCHANGE THROUGH SAID WALLS WITH THE CATALYST THEREIN AND TO AND FROM MEANS FOR REGULATING THE TEMPERATURE OF THE HEAT TRANSFER FLUID AND WHEREIN THE TRANSVERSE DIMENSIONS OF THE CATALYST MASS IN EACH SAID UNIT ARE NOT SUBSTANTIALLY LESS THAN 1 1/2 INCHES AND NOT SUBSTANTIALLY GREATER THAN 5 INCHES AND THE LENGTH OF SAID CATALYST MASS IN EACH SAID UNIT IS AT LEAST FOUR TIMES THE MINIMUM TRANSVERSE DIMENSIONS, WHEREBY THE DISTANCE HEAT OF CATALYSIS HAS TO TRAVEL THROUGH THE CATALYST MASS TO REACH SAID WALLS IS SO GREAT THAT OVERHEATING OF THE CATALYST MASS RESULTS WHEN THE PROCATALYSATE CONSISTS ESSENTIALLY OF PROHYDROGENATE AND HYDROGEN IN HYDROGENATING PROPORTIONS, THE IMPROVEMENT WHICH COMPRISES PREPARING A GASEOUS MIXTURE CONSISTING ESSENTIALLY OF PROHYDROGENATE VAPOR AND HYDROGEN IN HYDROGENATING PROPORTIONS IN ADMIXTURE WITH A RECYCLED INERT GAS IN THE PROPORTIONS OF AT LEAST 2 MOLS AND LESS THAN 10 MOLS OF INERT GAS FOR EACH MOL OF PROHYDROGENATE, PASSING SAID GASEOUS MIXTURE THROUGH SAID CATALYST MASS AT A RANGE WHICH GIVES SUBSTANTIALLY COMPLETE CONVERSION AND AT A PRESSURE SUFFICIENT TO SUPPRESS DEHYDROGENATION OF THE PRODUCT WHILE MAINTAINING SAID CATALYST MASS WITHIN ITS EFFECTIVE RANGE OF TEMPERATURE PRIMARILY BY REGULATING TEMPERATURE OF SAID HEAT TRANSFER FLUID. 